Stabilization of silver halide printout recording papers

ABSTRACT

A PROCESS IN WHICH A PRINTOUT RECORDING PAPER HAVING INCORPORATED DEVELOPING AGENT IS PHOTOLYTICALLY DEVELOPED AND A STABILIZING AGENT IS APPLIED SUBSEQUENT THERETO.

April 6, 1971 R, 5 m, 3,573,912

STABILIZATION 0F SILVER HALIDE PRINTOUT RECORDING PAPERS Original Filed Aug. 5, 1964 F INVENTOR.

nited States Patent Ofiice 3,573,912 Patented Apr. 6, 1971 Int. Cl. G03c 5/38, 5/32 US. CI. 96-61 16 Claims ABSTRACT OF THE DISCLOSURE A process in which a printout recording paper having incorporated developing agent is photolytically developed and a stabilizing agent is applied subsequent thereto.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of application Ser. No. 387,029, filed Aug. 3, 1964, now abandoned entitled Stabilization of Silver Halide Printout Recording Papers. Related disclosures can be found in Ser. No. 839,618, by J. H. Jacobs, filed Sept. 14, 1959, now U.S. Pat. No. 3,152,902.

BACKGROUND OF THE INVENTION (1) 'Field of the invention The field of art to which the invention pertains includes the field of photographic chemistry, processes and materials, particularly processes involving developing and ancillary operations and compositions therefor, including fixing and stabilization (2) Description of the prior art Silver halide printout emulsions are those in which visible traces of images recorded therein are produced without the necessity of adding further chemicals subsequent to exposure. These papers are used in oscillographs and the like and are particularly useful in rapid access applications where it is desired-to obtain a visible record of the results of a vibration, acceleration, etc., test as soon as possible after completion of the test. Such papers lend themselves extremely well to this application by virtue of the fact that production of a visible trace can be accomplished in approximately one second by means of forced latensification. A method and apparatus for accomplishing this result are described in US. Pats. 3,143,940 and 3,144,332, issued Aug. 11, 1964, to Richard P. Brown and John H. Jacobs and assigned to Bell & Howell Company, the assignee of the present application.

While the forced latensification process produces records which may be viewed immediately and which are stable for an appreciable length of time, their subsequent exposure to ambient light over period of weeks or months tends to reduce the contrast between the trace and the background due to a failure to completely inactivate the photosensitive emulsion during processing. Thus the visible or information image tends to merge into the emulsion background. Therefore, if the image recorded is to be retained for a considerable period of time, that is, months or years, or if better contrast is desired for purposes of making copies it is desirable to stabilize the image. A stabilized image as used in this context contemplates an image which has much less propensity to fade or become stained from prolonged storage or exposure than does the image in a normally latensified and unfixed printout paper.

Various processes for the stabilization of photosensitive printout emulsions of the silver halide type are known. One such process is known as the deep tank process in which the stabilization of the emulsion is accomplished in three steps: (a) bleaching the background of the emulsion without significantly affecting the visible image, (b) chemically developing the visible image and (c) stabilizing the resultant primary image in conventional stabilizing solutions. Other processes for treating these emulsions are similar to the development and fixation of any sliver halide emulsion. However, these processes are unsatisfactory in several respects including the fact that the processing steps are quite involved, the apparatus usually associated with these processes is cum bersome and expensive, the processing time is lengthy relative to the immediate availability of the visible record and one or more liquid baths are used with the resultant inconvenience of handling liquids.

SUMMARY OF THE INVENTION I have now found a new process that varies considerably from the processes described above and one that results in a substantial improvement in the quality of the stabilized print. Furthermore, this improvement in quality is not limited to a single paper or emulsion formula tion but is applicable to most known printout papers. In contrast to prior art systems where an ordinary printout emulsion was exposed and then introduced into a. processor for one or more treatment steps the present invention contemplates impregnating or incorporating a silver halide developing agent into the printout emulsion itself, prior to the processing step. Preferably, this incorporation is done during manufacture. Whereas the results of the deep tank process were sometimes better when the record was not intensified before introduction into the processing bath the present invention specifically requires an intensification step before the stabilization step.

The invention contemplates a process for producing visible and stable images in exposed silver halide print out recording papers in which a silver halide developing agent has been incorporated. The steps of the process comprise photolytic development of this exposed and treated paper to produce a visible image therein and thereafter the application of a silver halide stabilizing agent to the photolytically developed paper. The result is a visible image substantially stable to heat, light, atmosphere and humidity.

In a preferred form the invention contemplates the use of a gel web in which the stabilizer is incorporated in a suitable binder on a support sheet. For example, polyvinyl alcohol can be mixed with a polyhydric alcohol having six or less carbon atoms. The mixture of the two alcohols is heated. The stabilizer is dissolved in water and this solution is also heated. The two heated solutions are mixed and a sheet is coated with the mixture of water, stabilizer, polyvinyl alcohol and polyhydric alcohol. Thereafter the sheet is dried to leave on it a solid deposit of stabilizer. When such a web is used, the processing of silver halide printout papers is essentially dry thus eliminating liquid handling problems. Furthermore, the use of a system wherein liquids are not involved means that recording and stabilization can now be accomplished in many testing situations where a liquid processor would not be suitable, as for example in the testing of aircraft and submarines and other environments wherein the processing equipment may be subjected to various orientations and accelerations. The invention also contemplates an apparatus for use in conjunction with printout oscillographs in which the process of this invention is carried out.

The invention then represents a distinct advance over prior systems for stabilizing printout emulsions in several aspects. It it a process that produces a satisfactorily stabilized print in most printout emulsions. It is relatively inexpensive. As indicated above, when practiced with a gel web it is essentially dry lending itself to practically any testing situation. The apparatus included within the contemplation of the invention is adaptable equally to the stabilization of long or short lengths of printout paper. Where the deep tank process required a long length of leader attached to the short length of printout paper to be stabilized, with the apparatus of the present invention the short length is simply inserted into the receiving slot of the apparatus and is conveyed through the apparatus and brought in contact with a gel web and then is discharged from the apparatus in a dry and finished condition.

In addition to the application of a stabilizing agent by means of a gel web the invention is also adaptable to application of the agent in liquid form by means such as a coating roller, a brush or relatively wide-mouthed slit applicator or a spraying device. Furthermore this process is also adaptable to use with a deep tank process. In this instance however, a developer is incorporated in the printout emulsion prior to intensification, a step which is a distinct variation from the process as practiced previously. Again the result is a stable primary image with low background image.

BRIEF DESCRIPTION OF THE DRAWING The accompanying figure depicts an apparatus for stabilizing printout emulsions and in particular one which uses a web incorporating a silver halide stabilizing agent for application to a pretreated emulsion.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the figure there is shown in schematic form, an oscillograph 2, located adjacent the apparatus 4 used in carrying out the steps of the process of this invention. In the oscillograph a supply roll 6 of printout paper 8 impregnated with a silver halide developing agent is unreeled and carried past a recording location 10 where information in the form of time varying light signals from a source 12 is recorded on the printout paper. Subsequent to recording, the paper 8 is passed through an entrance 14 into the apparatus 4 where it is brought in contact with a heated platen 16 and subjected to intensifying radiation from light sources 18. Located adjacent the platen 16 is a supply roll 20 of a web containing the materials for stabilizing the exposed printout paper. This supply roll 20 is normally located within an air tight box 22 for preventing excessive evaporation from a gel formulation which is the usual vehicle for incorporating the stabilizing materials into the web 24. The printout paper 8 and gel web 24 are brought into contact simultaneously with contact to a heated drum 26. The drum serves the function of accelerating the release of the stabilizing agents from the web and optimizing the stabilization of the photolytically developed image in the printout paper. The sandwiched combination of printout paper and gel web pass around approximately 50% of the perimeter of the heated drum 26 and then separate with the spent web passing over a guide roller 28 and being collected on an auxiliary reel 30. At the same time the now stabilized printout paper is gathered on a reel 32.

The apparatus 4 is also capable of processing short lengths of photolytically developed printout paper. One way in which this is accomplished is by inserting the short length in the auxiliary entrance 34 provided in the apparatus 4 and engaging its leading edge With a fastening means (not shown) on an endless belt 36. The short length is then brought into contact with the gel web 24 by means of the belt 36 and pressure rollers 35 located at spaced intervals around the perimeter of the heated drum 26. The belt 36 carries the length of printout paper around the perimeter of the drum to the last pressure roller 38 where its direction of travel is reversed and it is passed over the pressure rollers on the side opposite the heated drum 26 back to the auxiliary entrance 34 where it is removed. Whether in short or long lengths, the record as it issues from the processing apparatus 4 is ready for storage as a permanent record or for use in providing a master sheet from which a number of copies can be made.

Where desired, a heating element is provided subsequent to the separation of the stabilizing Web to dry the record. The record is equally susceptible to air drying. When using a gel web in the apparatus of this invention such a drying step is not needed. But where the processing solution is applied in liquid form either by a roller, etc., or in a deep tank process, a drying means is normally desirable in order to issue a substantially dry record ready for use at the exit from the processing apparatus.

In process terms, the invention includes as one of its steps the intensification of the printout emulsion after it has been exposed to the information trace to be recorded. Intensification as used in this application refers to the process of amplification of the latent image by light whereby an invisible image recorded in a printout paper is made visible. One of the ways in which intensification is accomplished is by subjecting the exposed record to ambient light subsequent to recording. Under such conditions, the visible trace appears in most forms of printout paper in 60 seconds or less. This process can be speeded so that access to a visible record can be achieved in one second or less by means of forced intensification. This process calls for the step of drawing the printout paper after exposure over a heated platen whereby the temperature of the emulsion is raised to a point where the recording sensitivity of the paper is inactivated. Once it has been rendered insensitive to recording radiations the paper is subjected to high intensity light from a fluorescent or similar source whereby the information bearing trace is intensified, that is, the latent image centers in the silver halide specks are caused to grow to a point where they are visible to the human eye. Since the printout emulsion is insensitive to further recording by virtue of its elevated temperature the high intensity intensifying light does not cause the background to fog significantly, resulting in a desirable contrast between the visible trace and the background. Another way in which intensification is accomplished is to subject the exposed emulsion to a spectrum of radiations outside the emulsion recording sensitivity band. Such a method is described in US. Pat. 3,152,902, issued Oct. 13, 1964 to John H. Jacobs. In this process no particular form of intensification is preferred over any other, rather the important consideration is that the emulsion be intensified by one or a combination of the various known methods prior to the stabilization portion of the process.

An equally important step in the process is that a silver halide developing agent be incorporated within the printout emulsion prior to the time that it is intensified. While the previously known methods for stabilizing printout emulsions have also called for treating the emulsion with a developing agent this was normally done after the record had been exposed. The present invention contemplates incorporating a developing agent into the emulsion prior to intensification and preferably prior to exposure. Incorporation of the developer into the emulsion prior to intensification is thought to accomplish an important function in that by providing the developer in this particular manner, the amount of developer allowed to enter into the reaction is limited to an amount less than that needed to permit the exposed silver halide from going lnto solution. This limited amount of developer present in the emulsion has been found to be sufiicient to photolytically develop the image.

A further advantage of this process is that the developer is thoroughly mixed into the emulsion prior to the processing step thereby permitting the developing reaction to begin slightly in advance of the stabilizing reaction. In addition, in its preferred embodiment, this difference between initiation of development and stabilization is accentuated by processing the emulsion at an elevated temperature. It is well known in the photographic arts that an elevated temperature causes the development reaction to proceed at a faster rate than if performed at room temperature whereas there is relatively little change in the speed of the stabilization reaction due to a change in ambient temperature.

Incorporation of a developer in a printout emulsion is therefore an essential step in the process of this invention. While there are several ways in which the developer can be incorporated in the emulsion it is preferable that it be impregnated, that is, the emulsion be bathed or soaked in a developer solution prior to the recording exposure. In this connection it has been found that most of the conventional silver halide developing agents are suitable for use in the process of this invention, examples of these developers being: Phenidone, hydroquinone, ascorbic acid, metol, chlorhydroquinone, and glycine. While a single developer will produce satisfactory results, it has been found that optimum results are obtained by tailoring a combination of developers and other additives to the particular emulsion used. A typical formulation is as follows:

Parts by weight Phenidone 3 Hydroquinone 6 Ascorbic acid 7 Benzotriazole 3 Water to make 1000 parts of solution.

Benzotriazole is added to the above formulation to act as an antifoggant. A variation of 120% in the relative concentration of any one of the above constituents is permissible without significantly adverse results. Another example of a preferred developer combination is a mixture of Phenidone and hydroquinone in which the ratio of Phenidone to hydroquinone is twenty to one.

As indicated, impregnation of the developer into the paper prior to exposure is a preferred method of treating the emulsion since this means that a developer can be incorporated into the paper at the time of its manufacture. This, however, is not a controlling requirement for the process of this invention and in fact the developer can be incorporated into the emulsion after exposure so long as it is prior to intensification. Incorporation of a developer in this latter sequence, however, would add another step between exposure and production of a visible, stable record resulting in an undesirable increase in complexity of the processing apparatus and an increase in access time to the finished record. Hence, it is preferable to incorporate the developer into the emulsion at some point prior to exposure to the information image to be recorded in the oscillograph.

Subsequent to the preceding two steps the process calls for the application of a stabilizing agent to the record. Normally an alkali is combined with the stabilizing agent since most developers must be in an alkaline condition in order for the developing reaction to proceed. While certain developers such as amidol do work in the acid condition, an alkaline environment improves their performance. Hence, in its preferred form the invention contemplates application of a mixture of a silver halide stabilizing agent and an alkali following the intensification step of this process. Alkalis such as certain metal hydroxides are satisfactory for this purpose.

There are a number of stabilizing agents which are well known in the photographic art. Silver halide stabilizing agents as used herein refers to agents which perform the function of stabilizing a developed silver halide emulsion, not to stabilizing agents which are partly or entirely composed of a silver halide. These agents generally fall into two classes, those which reduce the silver to a water soluble complex and those which reduce the silver to a water insoluble complex. Either class is satisfactory for use in this process. Compounds which form soluble complexes include the various alkali thiosulfates, alkali thiocyanates, thiourea etc. Compounds which produce insoluble silver complexes with satisfactory stability belong to the general class of compounds represented by the general formula RSH, where R is any aliphatic, aromatic or heterocyclic compound with a free thiol (SH) group. As was true of the developers there is here also a preferred range of relative concentrations of the stabilizing agent and alkali depending on the emulsion and developer formulation used. A formulation for use with the first developing agent formulation given above is:

Parts by weight Sodium thiosulfate (stabilizing agent) 40 Diethanolamine (alkali) 20 Water to make 1000 parts of solution.

A variation of in the concentration of the above constituents is possible provided the two to one ratio of stabilizing agent to alkali is maintained.

The performance of the stabilizing agent can be enhanced by providing certain additives. Thus, materials such as wetting agents and photographic preservatives can be added to improve various aspects of the invention. For example, saponin can be used as a wetting agent and sodium sulfite as a preservative, in amounts hereinafter indicated.

As already indicated, application of the stabilizing agent and other additives (when used) can be accomplished in one of several ways e.g., a roller coater, a brush applicator, and the preferred method of application by means of a gel web. When using the web method, heat is normally applied to the sandwiched combination of emulsion and web. Although not essential, heat improves the appearance and quality of the record substantially by causing the gel to release sufficient amounts of moisture to thoroughly permeate the emulsion and optimize the action of the developer and stabilizer. Satisfactory results are obtained by raising the temperature of the emulsion and web to between approximately 100 and 200 F.

A satisfactory solution for depositing a layer of solid stabilizer is prepared from the ingredients listed in the following table:

Water to make 500 parts of solution In mixing the ingredients of the table, it is preferable to dissolve the carboxymethylcellulose (CMC) in cold glycerin and add the polyvinyl alcohol dispersed in about 100 parts of water. The mixture of polyvinyl alcohol, water, CMC and glycerin is then heated to about 180 F. The balance of the chemicals are dissolved in 180 parts of water, heated to about 180 F., and then mixed with the glycerin, polyvinyl alcohol, CMC and water. The CMC not only helps in dispersing the dissolving the polyvinyl alcohol, but it also aids the polyvinyl alcohol in adhering to the paper on which it is disposed. This reduces the tendency of the stabilizer layer to adhere to the silver halide emulsion when the sheets are pulled apart after the development of a visible image. This solution is applied as a thin film to a supporting sheet and dried to leave a deposit of a stabilizing compound and other chemicals on the sheet. In the formulation outlined in the table, the sodium thiosulfate is the stabilizing compound.

Another formulation where a stabilizing compound is to be incorporated within the second sheet or web is:

Parts by weight Solution A is prepared by adding the agar flakes to a heated mixture of Duponol ME and water with stirring. In Solution B the water is mixed into a heated solution containing the glycerin and locust bean gum. B is then added to A and to this is added:

Parts by weight Satisfactory Preferred range Sodium sulfite 7. 50 2. 5010. Sodium thiosulfate 50. 00 40. 00-60. 00

Water to make 400 parts of solution When mixed, the composition is coated while hot on a paper support and gels on cooling. The combination of agar flakes, glycerin and locust bean gum serves as the base or plasticizing material; glycerin also serves the function of a solvent for locust bean gum; sodium thiosulfate is the stabilizer; and the sodium sulfite aids in the stabilization process and prevents staining. Duponol MC is a wetting agent.

Examples of other materials that may be=substituted for the various constituents enumerated above are: for Duponol ME, saponin or Triton trade name for a wetting agent sold by Lohm & Haas Co.; for agar flakes, other marine colloids; for glycerin, methyl alcohol; for locust bean gum, methylcellulose or dextrine; for sodium sulfite and sodium thiosulfate, other preservatives and stabilizers Well known in the photographic arts.

It has been found that the previously described processing is not applicable to all printout emulsions. The emulsions on which this process does not work can be readily determined experimentally by processing a short length of the exposed emulsion according to the process of this invention. If this processing results in no image being produced or if a post-processing exposure to sunlight or other bright light source causes the emulsion to fog or blacken, the process is not applicable to that particular type of paper..

This process then is one for producing permanent records from images recorded in printout paper by means of a relatively simple inexpensive apparatus. The process is readily adaptable to most known varieties of printout paper without significant variation in formulations of the developing or stabilizing agents and at the same time lends itself in its preferred form to use in practically any recording environment.

I claim:

1. A process for producing visible and stable images in exposed silver halide printout recording papers in which a silver halide developing agent has been incorporated comprising:

photolytically developing the exposed paper to produce a substantially complete visible image therein, and thereafter applying a silver halide stabilizing agent to the photolytically developed paper whereby the visible image is rendered substantially stable to heat, light, atmos phere and humidity.

2. A process for producing visible and stable images in silver halide printout recording papers comprising:

(a) exposing the paper to light for the formation of a latent image,

(b) incorporating a silver halide developing agent into the exposed paper, thereafter (c) photolytically developing the exposed water to produce a substantially complete visible image therein, and thereafter (d) applying a silver halide stabilizing agent to the photolytically developed paper whereby the visible image is rendered substantially stable to heat, light, atmosphere and humidity.

3. A process for producing visible and stable images in silver halide printout recording papers comprising:

(a) incorporating a silver halide developing agent into the paper, thereafter (b) exposing the paper to light for the formation of a latent image,

(0) photolytically developing the exposed paper to produce a substantially complete visible image herein, and thereafter (d) applying a silver halide stabilizing agent to the photolytically developed paper whereby the visible image is rendered substantially stable to heat, light, atmosphere and humidity.

4. A process according to claim 1 wherein the silver halide stabilizing agent is applied by applying a web re leaseably incorporating a mixture thereof and an alkali to the photolytically developed paper.

5. A process according to claim 4 wherein heat is applied to the photolytically developed paper simultaneously with the application of the web.

6. A process according to claim 2 wherein the silver halide stabilizing agent is applied by applying heat and a web releasably incorporating a mixture thereof and an alkali to the photolytically developed paper.

7. A process according to claim 3 wherein the silver halide stabilizing agent is applied by applying heat and a web releasably incorporating a solution thereof and an alkali to the photolytically developed paper.

8. A process according to claim 1 wherein the silver halide stabilizing agent is applied by coating a solution including said agent and an alkali on the photolytically developed paper.

9. A process for producing visible and stable images in silver halide printout recording papers comprising:

(a) impregnating the paper with a silver halide developing agent,

(b) exposing the impregnated paper to light for the formation of a latent image,

(c) photolytically developing the exposed paper to produce a substantially complete visible image therein, and thereafter (d) coating a solution including a silver halide stabilizing agent and a alkali on the photolytically developed paper whereby the visible image is rendered substantially stable to heat, light, atmosphere and humidity.

10. A process according to claim 9 wherein in the coating is accomplished by means of a brush applicator.

11. A process according to claim 9 wherein the Coating is accomplished by means of a roller wetted with the solution.

12. A process according to claim 9 wherein the coating is accomplished by means of a spraying apparatus.

13. A process according to claim 9 wherein the coating is accomplished by means of a slit applicator.

14. A process according to claim 1 wherein the silver halide stabilizing agent is applied by passing the photolytically developed paper through a bath containing a solution including said agent and an alkali.

15. A process according to claim 2 wherein the silver halide stabilizing agent is applied by passing the photolytically developed paper through a bath containing a solution including said agent and an alkali.

16. A process according to claim 3 wherein the silver halide stabilizing agent is applied by passing the photo- 9 10 lytically developed paper through a bath containing a Photographic Science and Engineering, vol. 5, N0. 1, solution including said agent and an alkali solution. Jan-Feb. 1961.

L. 'F. A. Masonz, Photographic Processing Chemistry, References Cited 1966, pp, 125, 126.

UNITED STATES PATENTS 5 NORMAN G. TORCHIN, P i 3,035,912 5/1962 Massena et a1 96--27 f Exammer 3 34 94 10 19 7 Jones 96 29 E. C. KIMLIN, Assistant Examiner 3,253,923 5/1966 Glover et a1 96--60 Us cl- X'R.

OTHER REFERENCES 10 60 John H. Jacobs, An Investigation of Printout Paper, 

